You should also make sure that there is sufficient space on the
hard drive partition of the backup target.

NDB does not support repeatable
reads, which can cause problems with the restoration process.
Although the backup process is “hot”, restoring a
MySQL Cluster from backup is not a 100% “hot”
process. This is due to the fact that, for the duration of the
restore process, running transactions get nonrepeatable reads
from the restored data. This means that the state of the data is
inconsistent while the restore is in progress.